diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index 4589dab409..815410969c 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -223,6 +223,13 @@ class DeviceHandler(BaseHandler):
 
     @defer.inlineCallbacks
     def get_user_ids_changed(self, user_id, from_token):
+        """Get list of users that have had the devices updated, or have newly
+        joined a room, that `user_id` may be interested in.
+
+        Args:
+            user_id (str)
+            from_token (StreamToken)
+        """
         rooms = yield self.store.get_rooms_for_user(user_id)
         room_ids = set(r.room_id for r in rooms)
 
diff --git a/synapse/storage/stream.py b/synapse/storage/stream.py
index 3765d0095c..200d124632 100644
--- a/synapse/storage/stream.py
+++ b/synapse/storage/stream.py
@@ -247,6 +247,10 @@ class StreamStore(SQLBaseStore):
     def get_rooms_that_changed(self, room_ids, from_key):
         """Given a list of rooms and a token, return rooms where there may have
         been changes.
+
+        Args:
+            room_ids (list)
+            from_key (str): The room_key portion of a StreamToken
         """
         from_key = RoomStreamToken.parse_stream_token(from_key).stream
         return set(